Ion implantation process is used in manufacturing of, among others, electrical and optical devices. It is used for implanting impurities or dopants to alter one or more properties of a substrate. In integrated circuit (IC) manufacturing, the substrate may be a silicon substrate, and the process may be used alter the electrical property of the substrate. In solar cell manufacturing, the process may be used to alter the optical and/or electrical property of the substrate. As the impurities or dopants implanted into the substrate may affect the performance of the final device, a precise and uniform implant profile is desired.
Referring to FIG. 1, there is shown a conventional indirectly heated cathode (IHC) ion source 100 and an extraction system 112 of a conventional ion implantation system that may be used to implant impurities or dopants. As illustrated in FIG. 1, a typical IHC ion source 100 includes an ion source chamber 102 comprising one or more conductive chamber walls 102a defining an ion generation region 104. The ion source chamber 102 also includes an extraction aperture 102b. At one side of the ion source chamber 102, there may be a cathode 106 and a filament 108. Opposite to the cathode 108, there may be a repeller 110.
A feed source 114 containing feed material may be coupled to the ion source chamber 102. The feed material may contain desired implanter species (e.g. dopant species).
Near the extraction aperture 102b of the ion source chamber 102, there may be an extraction system 112. The extraction system 112 may comprise a suppression electrode 112a positioned in front of the extraction aperture 102b and a ground electrode 112b. The suppression electrode 112a may be electrically coupled to a suppression power supply 116a, whereas the ground electrode 112b may be electrically coupled to an extraction power supply 116a. Each of the suppression electrode 112a and the ground electrode 112b has an aperture aligned with the extraction aperture 102b for extraction of the ions 20 from the ion source chamber 102.
In operation, the feed material is introduced into the ion source chamber 102 from the feed source 110. The filament 108, which may be coupled to a power supply (not shown), is activated. The current supplied to the filament 108 may heat the filament 108 and cause thermionic emission of electrons. The cathode 106, which may be coupled to another power supply (not shown), may be biased at much higher potential. The electrons emitted from the filament 108 are then accelerated toward and heat the cathode 106. The heated cathode 106, in response, may emit electrons toward the ion generation region 104. The chamber walls 102a may also be biased with respect to the cathode 106 so that the electrons are accelerated at a high energy into the ion generation region 104. A source magnet (not shown) may create a magnetic field B inside the ion generation region 104 to confine the energetic electrons, and the repeller 110 at the other end of the ion source chamber 102 may be biased at a same or similar potential as the cathode 106 to repel the energetic electrons.
Within the ion generation region 104, energetic electrons may interact and ionize the feed material to produce plasma 10 containing, among others, ions of desired species 20 (e.g. desired dopants or impurities). The plasma 10 may also contain undesired ions or other fragments of the feed materials.
The extraction power supply 116b may provide an extraction voltage to the ground electrode 112b for extraction of the ion beam 20 from the ion source chamber 102. The extraction voltage may be adjusted according to the desired energy of the ion beam 20. The suppression power supply 116a may bias the suppression electrode 112a to inhibit movement of electrons within the ion beam 20
In order to manufacture devices with optimal performance, it is generally desirable to process the substrate with uniform ion beam with high beam current (i.e. high concentration or dose of desired ions). Moreover, it is desirable to implant the substrate with an ion beam having low beam glitch rate. A glitch is defined as a sudden degradation in the beam quality during an ion implantation operation. If the implantation process is interrupted or affected by a glitch, the substrate may be negatively affected or even potentially rendered unusable. A low beam current may increase the time necessary to achieve proper implant dose in the substrate and lead to lower throughput. Meanwhile, non-uniform beam and/or high glitch rate may result in non-uniform dopant profile. Such deficiencies which are observed often in the ion implantation system with conventional IHC ion sources may lower the throughput and/or increase the manufacturing cost of the devices.
The above deficiencies may be caused by, among others, films or deposits formed on the inner wall of the ion source chamber 102, extraction aperture 102b, and the extraction electrodes 112. As noted above, the plasma 10 generated in the ion generation region 104 contains highly reactive ions and other fragments of the feed material. Such ions and fragments may etch, sputter, or otherwise react with the materials in the ion source chamber 100. The etched materials may then condense to form films or deposits on the ion source chamber wall 102a, the extraction aperture 102b, and the extraction electrodes 112. The films or deposits may block the extraction aperture 102b to cause a non-uniform ion beam 20 having different doses in different regions of the ion beam 20. In addition, the ion beam 20 extracted may have low beam current. In some cases, the films or deposits may be electrically conductive and provide ignition points in which micro/macro arcing may occur. Such arcing may lead to beam glitches.
One way to decrease the rate of such a defective ion beam 20 is to periodically replace the ion source 100 with a new/clean ion source 100. However, replacement of ion source 100 requires the entire ion source 100 and vacuum pumping system attached to the ion source 100 to be powered down. Moreover, the ion source 102 must be manually replaced. Further, the process by which the ion source 100 may be cleaned is a labor intensive process. Accordingly, frequent replacement of the ion source 100 may lower the efficiency of the ion implantation process.
With increased need for higher ion beam current for manufacturing advanced electronic and solar cell devices, greater amount of feed material is introduced and ionized in the ion source chamber 100. As a result, higher rate of defective beam is observed during ion implantation process. The conventional IHC ion sources may have low performance and low lifetime, and processing substrates in a system containing the conventional IHC ion source may be less than optimal.
In view of the foregoing, it would be desirable to provide a new technique is needed.